1. Field of the Invention
The present invention relates to an object information acquiring apparatus.
2. Description of the Related Art
As one of methods of calculating an optical property value such as an absorption coefficient in a living organism, there is photoacoustic tomography (hereinafter, PAT) that makes use of a characteristic of an ultrasound wave that scatters less in the living organism than light (Non Patent Literature 1: M. Xu, L. Wang “Photoacoustic imaging in biomedicine”, Review of scientific instruments, 77, 041101(2006)). When pulsed light generated from a light source is irradiated on the living organism, the light propagates while diffusing in the living organism. A light absorber included in the living organism absorbs the propagated light and generates an acoustic wave (typically, an ultrasound wave). By receiving the acoustic wave with a probe and analyzing the received signal, it is possible to obtain an initial sound pressure distribution caused by the absorber in the living organism. An absorption coefficient distribution can be obtained by taking into account a distribution of the light with respect to the initial sound pressure distribution.
The sound pressure of the acoustic wave in the PAT is proportional to an amount of local light that reaches the light absorber. The light irradiated on the living organism suddenly attenuates in the living organism because of the scattering and the absorption. Therefore, the sound pressure of the acoustic wave generated in a deep tissue in the living organism substantially attenuates according to the distance from the light irradiated region. Therefore, in order to obtain information concerning a living organism deep part, it is necessary to reduce the thickness of an object region. As an example, in Susanne E. et al. “First clinical trials of the Twente Photoacoustic Mammoscope (PAM)” (Non Patent Literature 2), an object is held and pressured by two holding plates to reduce the thickness of the object. When the holding plates are used, in order to suppress deformation due to the pressuring, in general, a supporting unit with high rigidity made of metal, ceramic, or the like is provided around the holding plates.
In a photoacoustic signal acquiring apparatus, when direct light from a light source or light propagated in the living organism is irradiated on a probe surface, an acoustic wave is generated on the probe surface and the acoustic wave causes a noise. The acoustic wave generated on the probe surface is received by the probe first. An acoustic wave from the living organism is received by the probe before a response to a signal of the received acoustic wave ends. In other words, the signal received by the probe is a signal on which noise is superimposed. In the photoacoustic signal acquiring apparatus, when information concerning the inside of an object is converted into an image on the basis of the signal received by the probe, noise caused by an acoustic wave generated in the supporting unit is an artifact. As a result, accuracy in using the image for medical diagnosis is deteriorated.
Therefore, Japanese Patent Application Laid-Open No. 2010-75681 (Patent Literature 1) discloses an example in which a light reflecting member is provided on a probe surface, whereby an acoustic wave generated on the probe surface by diffused light emitted to the outside of a living organism is reduced to reduce noise.
Patent Literature 1: Japanese Patent Application Laid-Open No. 2010-75681
Non Patent Literature 1: M. Xu, L. Wang “Photoacoustic imaging in biomedicine”, Review of scientific instruments, 77, 041101(2006)
Non Patent Literature 2: Susanne E. et al. “First clinical trials of the Twente Photoacoustic Mammoscope (PAM)”